Ultrasonic instruments, including both hollow core and solid core instruments, are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments, are advantageous because they may be used to cut and/or coagulate organic tissue using energy in the form of mechanical vibrations transmitted to a surgical end effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels and using a suitable end effector, may be used to cut, dissect, elevate or cauterize tissue or to separate muscle tissue off bone. Such instruments may be used for open procedures or minimally invasive procedures, such as endoscopic or laparoscopic procedures, wherein the end effector is passed through a trocar to reach the surgical site.
Activating or exciting the end effector (e.g., cutting blade) of such instruments at ultrasonic frequencies induces longitudinal vibratory movement that generates localized heat within adjacent tissue, facilitating both cutting and coagulation. Because of the nature of ultrasonic instruments, a particular ultrasonically actuated end effector may be designed to perform numerous functions, including, for example, cutting and coagulation.
Ultrasonic vibration is induced in the surgical end effector by electrically exciting a transducer, for example. The transducer may be constructed of one or more piezoelectric or magnetostrictive elements in the instrument hand piece. Vibrations generated by the transducer section are transmitted to the surgical end effector via an ultrasonic waveguide extending from the transducer section to the surgical end effector. The waveguides and end effectors are designed to resonate at the same frequency as the transducer. Therefore, when an end effector is attached to a transducer the overall system frequency is the same frequency as the transducer itself.
The zero to peak amplitude of the longitudinal ultrasonic vibration at the tip, d, of the end effector behaves as a simple sinusoid at the resonant frequency as given by:d=A sin(ωt)where:ω=the radian frequency which equals 2π times the cyclic frequency, f, andA=the zero-to-peak amplitude.The longitudinal excursion is defined as the peak-to-peak (p-t-p) amplitude, which is just twice the amplitude of the sine wave or 2A.
Ultrasonic surgical instruments may be divided into two types, single element end effector devices and multiple-element end effector devices. Single element end effector devices include instruments such as scalpels and ball coagulators. Single-element end effector instruments have limited ability to apply blade-to-tissue pressure when the tissue is soft and loosely supported. Sometimes, substantial pressure may be necessary to effectively couple ultrasonic energy to the tissue. This inability to grasp the tissue results in a further inability to fully coapt tissue surfaces while applying ultrasonic energy, leading to less-than-desired hemostasis and tissue joining. In these cases, multiple-element end effectors may be used. Multiple-element end effector devices, such as clamping coagulators, include a mechanism to press tissue against an ultrasonic blade that can overcome these deficiencies.
Many surgical procedures utilizing harmonic and non-harmonic instruments create extraneous tissue fragments and other materials at the surgical site. If this material is not removed, it may obstruct the clinician's view and also may interfere with the blade or other end effector of the surgical device. To remove the material, the clinician must remove the instrument from the surgical area and introduce an aspiration tool. This can break the clinician's concentration and also contribute to physical and mental fatigue.
Also, in some surgical procedures, it is desirable to remove a core or other integral portion of tissue. In these procedures, the clinician uses a first instrument to grasp and sometimes cut an outline of the tissue to be removed. Then a second instrument is utilized to remove the tissue from surrounding material, often while the tissue is still grasped by the first instrument. This process may be particularly challenging for clinicians because it can require the use of multiple instruments, often simultaneously. Also, many coring procedures are performed at very delicate portions of the anatomy that require precise cuts.
In addition, existing harmonic instruments allow the clinician to turn them on or off, but provide limited control over the power delivered to tissue once the instrument is turned on. This limits the usefulness of harmonic instruments in delicate surgical procedures, where fine cutting control is required.